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Tuesday, July 04, 2017

Roman Concrete for Rising Seas?

ViaBBC Science, a story appealing at once to my fascination with all things Roman as to my passion for all things ecological:

Ancient sea walls built by the Romans used a concrete made from lime and volcanic ash to bind with rocks. Now scientists have discovered that elements within the volcanic material reacted with sea water to strengthen the construction. They believe the discovery could lead to more environmentally friendly building materials. Unlike the modern concrete mixture which erodes over time, the Roman substance has long puzzled researchers.
Rather than eroding, particularly in the presence of sea water, the material seems to gain strength from the exposure... "Contrary to the principles of modern cement-based concrete," said... Marie Jackson from the University of Utah, US, "the Romans created a rock-like concrete that thrives in open chemical exchange with seawater." ... The ancient mixture differs greatly from the current approach. Modern buildings are constructed with concrete based on Portland cement... The process of making cement has a heavy environmental penalty, being responsible for around 5% of global emissions of CO2. So could the greater understanding of the ancient Roman mixture lead to greener building materials? Prof Jackson is testing new materials using sea water and volcanic rock from the western United States. Speaking to the BBC earlier this year, she argued that the planned Swansea tidal lagoon should be built using the ancient Roman knowledge of concrete. "Their technique was based on building very massive structures that are really quite environmentally sustainable and very long-lasting," she said. "I think Roman concrete or a type of it would be a very good choice [for Swansea]. That project is going to require 120 years of service life to amortise [pay back] the investment. "We know that Portland cement concretes contain steel reinforcements. Those will surely corrode in at least half of that service lifetime." There are a number of limiting factors that make the revival of the Roman approach very challenging. One is the lack of suitable volcanic rocks. The Romans, the scientists say, were fortunate that the right materials were on their doorstep. Another drawback is the lack of the precise mixture that the Romans followed. It might take years of experimenting to discover the full formula.